Platemaking method, platemaking device, and printing press

ABSTRACT

There is provided a platemaking method of forming relief based on relief pattern data in a printing plate to be pressed on a printing matter, and the platemaking method includes steps of: estimating distribution of printing pressure of the printing plate pressed on the printing matter on the basis of image data and distribution data of plate thickness; calculating an amount of correction of engraving shape data on the basis of the distribution of printing pressure; correcting the engraving shape data on the basis of the amount of correction; and acquiring exposure amount data from the engraving shape data corrected. It is possible to form relief in consideration of deformation of a printing plate in accordance with the distribution of printing pressure in the printing plate to favorably print and reproduce an image on a printing medium.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of PCT International Application No.PCT/JP2014/058439 filed on Mar. 26, 2014, which claims priority under 35U.S.C§119(a) to Japanese Patent Application No. 2013-074303 filed onMar. 29, 2013. Each of the above application(s) is hereby expresslyincorporated by reference, in its entirety, into the presentapplication.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a platemaking method, a platemakingdevice, a printing press, and a printing plate, and more particularly toa printing plate that is made by applying laser engraving to aflexographic plate, for example.

2. Description of the Related Art

Printing letterpress is widely adopted in the field of printing, such asflexographic printing, and particularly in recent years, theflexographic printing has received widespread attention as aneco-friendly printing method.

In the flexographic printing, printing is performed by using a soft andflexible plate and ink (such as water-based ink, and UV ink). The plateused in the flexographic printing is deformed in accordance withprinting pressure (pressed amount) due to its flexibility. Accordingly,a flexographic printing plate enables favorable transfer printing to beapplied also to a printing medium, such as corrugated cardboard whosesurface has asperities, by properly following the surface to be broughtinto close contact with the surface.

Japanese Patent Application Laid-Open No. 2011-224878 (hereinafterreferred to as PTL 1) discloses printing letterpress to be adopted inflexographic printing. The printing letterpress has a plurality of kindsof dot main protrusion each of whose height in a printing surface isdifferent from each other in a tint area. In PTL 1, local expansion of asmall dot is avoided to eliminate occurrence of non-printing failurenear a solid portion, thereby eliminating instability in printingpressure caused by reducing height of a part of the dot protrusions.

Japanese Patent Application Laid-Open No. 2012-074281 (hereinafterreferred to as PTL 2) discloses a printing plate for preventing atransfer area formed on a surface of an object to be transferred bytransferring a pattern area of the printing plate from being formed in atrapezoid shape stretched from the pattern area. In the printing plate,there is provided a pattern area reduced from pattern area data, and inthe pattern area, a reduction ratio of a portion existing on a front endside in a rotation direction of a plate cylinder, to which transferprinting is to be applied earlier, is lower than a reduction ratio of aportion existing on a rear end side therein, to which the transferprinting is to be applied later.

SUMMARY OF THE INVENTION

As ideal plate deformation characteristics of a printing plate to beused in flexographic printing or the like, it is desirable that vicinityof a surface (a portion required for ink transfer) of the printing plateis not deformed by printing pressure during printing, but the printingplate (a relief portion) is deformed so as to sink only in a heightdirection. Unfortunately, in actual printing, the printing plate isdeformed from vicinity of the surface of the printing plate.

This kind of deformation of a printing plate varies in accordance withthe amplitude of printing pressure occurring between a printing mediumand the printing plate. The printing pressure between the printing plateand the printing medium varies depending on a relief shape of theprinting plate, and is affected by a size of contact area between them.That is, in the printing plate, there is a tendency to allow printingpressure to increase more in an area (such as a dot (isolated point)forming area) having a relatively small contact area due toconcentration of pressure than in an area (such as a solid fill area)having a relatively large contact area. Accordingly, there is a tendencyto allow deformation of a plate to increase more in an area having arelatively small contact area than in an area having a relatively largecontact area to cause a printed image on a printing medium to expand.

In addition, deviation in printing pressure is affected by not only asize (relief shape) of contact area of an area of interest but also asummation (relief shape) of contact area in a peripheral area includingthe area of interest, so that the printing pressure (a pressed amount ofa printing plate) in the area of interest varies depending on a kind ofperipheral image (such as a solid region, a dot percent, and a whitepatch).

Accordingly, in an area (such as an isolated point) with a small contactarea, a way of expansion of a printed image on a printing medium isdifferent between a case where there is an area (such as a solid fill)with a large contact area in neighborhood and a case other than that.Thus, image density reproduced on a printing medium may vary dependingon a kind of relief of a peripheral area even in a dot formation areawith the same contact area ratio to cause various kinds of degradationin image quality, such as that an isolated point or a thin line expands,to occur in a different region in the image. As above, in a conventionalflexographic printing technique, it is difficult to ensure uniformprinting reproducibility in an image because a dot and a thin linebecome thick or thin more than expected.

In addition, also in a case where there are variations in thickness of aprinting plate, reproducibility of a printed image on a printing mediumis unstable. If there is thickness distribution in a printing plate initself due to a manufacturing error, or the like, a position (height) ofthe apex of relief at each of a thick portion and a thin portion of theprinting plate is different even if having the same relief (engravingstructure). That is, the position of the apex of relief at the thickportion becomes relatively high, and the position of the apex of reliefat the thin portion becomes relatively low. Thus, in a printing platehaving variations in thickness, printing pressure changes in accordancewith distribution of the thickness, so that a way of expansion of animage reproduced on a printing medium differs depending on platethickness.

The present invention is made in light of the above-mentionedcircumstances, and it is an object of the present invention to provide atechnique capable of reproducing a favorable image on a printing mediumby determining relief (engraving shape) of a printing plate inconsideration of deformation of the printing plate in accordance withdistribution of printing pressure.

One aspect of the present invention relates to a platemaking method offorming relief based on relief pattern data in a printing plate to bepressed on a printing medium, and the platemaking method includes thesteps of: calculating relief pattern data on the basis of image data;acquiring distribution data of plate thickness showing distribution ofplate thickness of the printing plate; estimating distribution ofprinting pressure of the printing plate pressed on a printing medium onthe basis of the image data and the distribution data of platethickness; calculating an amount of correction of the relief patterndata on the basis of the distribution of printing pressure; andcorrecting the relief pattern data on the basis of the amount ofcorrection.

According to the present aspect, distribution of printing pressure isaccurately acquired from image data and distribution data of platethickness, and an amount of correction of relief pattern data iscalculated on the basis of the distribution of printing pressure so thatthe relief pattern data is corrected on the basis of the amount ofcorrection calculated. Thus, it is possible to perform correction of therelief pattern data and determination of relief in consideration ofdeformation of a printing plate in accordance with the distribution ofprinting pressure to enable a favorable image to be printed andreproduced on a printing medium.

The relief pattern data may include arbitrary relief pattern data, and,for example, may appropriately include a dot printing relief, a printingof a protruded thin line relief, a solid fill printing relief, and aprinting relief of other shapes.

It is preferable that the distribution of printing pressure is estimatedon the basis of an area ratio of a portion with which the printingmedium is to be brought into contact within a predetermined range of theprinting plate.

The printing pressure varies in accordance with a ratio of a contactarea (ground area) between the printing plate and the printing medium.Thus, according to the present aspect, it is possible to accuratelyestimate distribution of printing pressure.

It is preferable that the relief includes a plurality of protrusions,and the relief pattern data includes height data of the plurality ofprotrusions and shape data of the plurality of protrusions, and also theamount of correction of the relief pattern data relates to at least anyone of the height data and the shape data of the plurality ofprotrusions.

According to the present aspect, it is possible to correct the relief onthe basis of at least any one of height and shape of the protrusions.

It is preferable that each of the plurality of protrusions includes abase and a tip provided on the base, on which a printing medium ispressed, and that the shape data of the plurality of protrusionsincludes at least shape data of the tip.

According to the present aspect, it is possible to correct the reliefformed on the printing plate on the basis of the shape data of the tipof the protrusion. “The tip of the protrusion” means an edge including aportion (face) that is to be pressed on the printing medium duringprinting.

It is preferable that the shape data of the tip of each of the pluralityof protrusions includes data on a portion of the tip that is to bebrought into contact with the printing medium during printing.

According to the present aspect, it is possible to correct the reliefformed on the printing plate on the basis of the data on a portion(face) of the tip of the protrusion that is to be brought into contactwith the printing medium during printing.

It is preferable that the plurality of protrusions includes a base and atip provided on the base, on which a printing medium is pressed, andthat the height data of the plurality of protrusions relates to any oneof tip height, base height, and entire height of the tip and the base.

According to the present aspect, it is possible to correct the reliefformed on the printing plate on the basis of at least any one of the tipheight, the base height, and the entire height of the tip and the baseof the protrusions.

It is preferable that the relief includes a plurality of protrusions,and the relief pattern data includes volume data of the plurality ofprotrusions, the amount of correction of the relief pattern data relatesto the volume data of the plurality of the protrusions.

According to the present aspect, it is possible to correct the reliefformed on the printing plate on the basis of the volume data of theprotrusions.

The relief pattern data and the amount of correction of the reliefpattern data may directly use the volume data of the protrusions, or mayuse “an element (such as cross section size, cross-sectional area, andheight) that defines the volume of the protrusions”, which canindirectly express the volume data of the protrusions.

It is preferable that the platemaking method further includes the stepof forming the relief on the printing plate on the basis of the reliefpattern data corrected.

According to the present aspect, it is possible to print and reproduce afavorable image on the printing medium with the printing plate for whichcorrection of the relief pattern data and determination of the reliefare performed in consideration of deformation of the printing plate inaccordance with distribution of printing pressure.

It is preferable that the relief is formed on the printing plate byexposure processing with respect to the printing plate, and exposurecharacteristics related to a thickness direction of the printing plateare derived on the basis of the distribution data of plate thickness sothat the relief is formed on the printing plate by the exposureprocessing in consideration of the exposure characteristics.

According to the present aspect, since the relief is formed by theexposure processing in consideration of “the exposure characteristicsrelated to the thickness direction of the printing plate” derived on thebasis of the distribution data of plate thickness, it is possible toform the relief in accordance with the exposure characteristics, withhigh accuracy. Thus, even if plate thickness of the printing plate isnot uniform, it is possible to accurately form the relief capable ofreproducing a desired image on the printing plate.

The term, “exposure characteristics”, means characteristics that mayvary in the thickness direction of the printing plate, and may includevarious factors such as exposure conditions that may affect the exposureprocessing. For example, “a diameter of an exposure beam” used in theexposure processing, and the like, may be adopted as the exposurecharacteristics.

Another aspect of the present invention relates to a platemaking devicethat forms relief based on relief pattern data in a printing plate to bepressed on a printing medium, and the platemaking device includes: arelief calculation unit that calculates relief pattern data on the basisof image data; a plate thickness distribution acquisition unit thatacquires distribution data of plate thickness showing distribution ofplate thickness of a printing plate; a printing pressure distributionestimation unit that estimates distribution of printing pressure of theprinting plate pressed on the printing medium on the basis of the imagedata and the distribution data of plate thickness; a correction amountcalculation unit that calculates an amount of correction of the reliefpattern data on the basis of the distribution of printing pressure; anda data correction unit that corrects the relief pattern data on thebasis of the amount of correction.

Yet another aspect of the present invention relates to a printing pressthat includes the platemaking device described above, and a printingunit that presses the printing plate in which relief is formed by theplatemaking device on the printing medium.

Yet another aspect of the present invention relates to a printing platein which relief is formed, and the relief is formed by the steps of:calculating relief pattern data on the basis of image data; acquiringdistribution data of plate thickness showing distribution of platethickness of the printing plate; estimating distribution of printingpressure of the printing plate pressed on a printing medium on the basisof the image data and the distribution data of plate thickness;calculating an amount of correction of the relief pattern data on thebasis of the distribution of printing pressure; correcting the reliefpattern data on the basis of the amount of correction; and forming therelief on the basis of the relief pattern data corrected.

According to the present invention, image contents and distribution ofplate thickness are analyzed to estimate distribution of printingpressure so that data correction is performed so as to correctdeformation of a printing plate estimated from the distribution ofprinting pressure, whereby relief can be formed in consideration of thedistribution of printing pressure. Accordingly, it is possible to obtaina stably favorable image printed matter as targeted regardless of imagecontents even if plate thickness is not uniform.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of a configuration of a main section of aflexographic printing press.

FIG. 2 is an enlarged view of a contact portion between a flexographicprinting plate and a printing medium during printing.

FIG. 3 is a plan view showing an example of a laser engraving machinethat forms a relief on a flexographic printing plate.

FIG. 4 is a plan view showing an example of a relief formed in a part ofa flexographic printing plate.

FIG. 5 shows an example of a relationship between areas of theflexographic printing plate shown in FIG. 4 and an amount of depressionduring printing.

FIG. 6 shows an example of a relationship between the areas of theflexographic printing plate shown in FIG. 4 and printing pressure duringprinting.

FIG. 7 is a plan view of a printing medium that shows an actual printedimage in a case where normal printing is performed with the flexographicprinting plate shown in FIG. 4, and that particularly shows a printedimage obtained on the assumption that plate thickness is uniformthroughout the flexographic printing plate.

FIG. 8 shows distribution of plate thickness of a flexographic printingplate in accordance with FIGS. 4 to 6.

FIG. 9 is a plan view of a printing medium showing an ideal printedimage targeted when ideal printing is performed with the flexographicprinting plate shown in FIG. 4.

FIG. 10 is a plan view of a printing medium that shows an actual printedimage in a case where normal printing is performed with the flexographicprinting plate shown in FIG. 4, and that particularly shows a printedimage obtained on the assumption that plate thickness is not uniformthroughout the flexographic printing plate.

FIG. 11 is a block diagram showing a configuration of a flexographicprinting system in accordance with one embodiment of the presentinvention.

FIG. 12 is a functional block diagram showing an example of aconfiguration of the exposure amount data creation unit of FIG. 11.

FIG. 13 is a functional block diagram showing an example of aconfiguration of an engraving shape data correction unit of FIG. 12.

FIG. 14 is a flow chart that shows an outline of a flow of processing inthe engraving shape data correction unit and the exposure amount dataconverter, and that shows an example of estimating distribution ofprinting pressure on the basis of image data before being converted intoengraving shape data.

FIG. 15 shows change in a diameter of a laser (exposure beam) used inthe laser engraving machine.

FIG. 16 is a flow chart that shows an outline of a flow of processing inthe engraving shape data conversion unit, the engraving shape datacorrection unit, and the exposure amount data converter, and that showsan example of estimating distribution of printing pressure on the basisof engraving shape data.

FIG. 17 is a flow chart that describes an example of a process ofcalculating distribution of printing pressure on the basis of image data(engraving shape data) to calculate an amount of correction based on thedistribution of printing pressure.

FIG. 18 shows an example of an image to describe an ROI.

FIG. 19 shows an example of a correspondence relation between a groundarea ratio in an ROI and a pressed amount.

FIG. 20 shows an example of a correspondence relation between “a pressedamount at a position of interest (a pixel of interest)” and “the amountof correction of engraving shape data at the position of interest”.

FIG. 21 is a table (conversion table) showing an example of an exposuretable to achieve shape correction.

FIG. 22 is a table showing an exposure conversion table to achieve shapecorrection corresponding to a laser beam diameter.

FIG. 23 shows an example of image data (1-bit image data) before beingconverted into engraving shape data.

FIG. 24 shows an example of engraving shape data that can be acquiredfrom the image data of FIG. 23.

FIG. 25 shows an example of “engraving shape data after correction” thatcan be acquired by correcting the engraving shape data shown in FIG. 24on the basis of distribution of printing pressure.

FIG. 26 shows another example of the “engraving shape data aftercorrection” that can be acquired by correcting the engraving shape datashown in FIG. 24 on the basis of distribution of printing pressure.

FIG. 27 is a perspective view that shows an appearance of an example ofa relief formed in a part of a flexographic printing plate, and thatshows an example of the relief (protrusions) created on the flexographicprinting plate by engraving on the basis of engraving shape data towhich correction in consideration of distribution of printing pressureis not applied.

FIG. 28 is a perspective view that shows an appearance of an example ofa relief formed in a part of a flexographic printing plate, and thatshows an example of the relief (protrusions) created on the flexographicprinting plate by engraving on the basis of engraving shape data towhich the correction in consideration of distribution of printingpressure is applied.

FIG. 29 is an external view of protrusions to describe an example ofcorrecting an engraving shape (tip shape) of a small dot in dots inaccordance with distribution of printing pressure, and includes: aportion (a) that shows a protrusion in a case where printing pressuremore than normal is applied; a portion (b) that shows a protrusion in acase where normal printing pressure is applied; and a portion (c) thatshows a protrusion in a case where printing pressure less than normal isapplied.

FIG. 30 is an external view of protrusions to describe an example ofcorrecting an engraving shape (protrusion height) of a small dot in dotsin accordance with distribution of printing pressure, and includes: aportion (a) that shows a protrusion in a case where printing pressuremore than normal is applied; a portion (b) that shows a protrusion in acase where normal printing pressure is applied; and a portion (c) thatshows a protrusion in a case where printing pressure less than normal isapplied.

FIG. 31 is an external view of protrusions to describe an example ofcorrecting an engraving shape (protrusion tip volume) of a small dot indots in accordance with distribution of printing pressure, and includes:a portion (a) that shows a protrusion in a case where printing pressuremore than normal is applied; a portion (b) that shows a protrusion in acase where normal printing pressure is applied; and a portion (c) thatshows a protrusion in a case where printing pressure less than normal isapplied.

FIG. 32 is an external view of protrusions to describe an example ofcorrecting a relief engraving shape (tip shape) for printing of aprotruded thin line in accordance with distribution of printingpressure, and includes: a portion (a) that is a perspective view thatshows an appearance of a protrusion for printing of a protruded thinline; a portion (b) that is a cross-sectional view of a protrusion in acase where printing pressure more than normal is applied; a portion (c)that is a cross-sectional view of a protrusion in a case where normalprinting pressure is applied; and a portion (d) that is across-sectional view of a protrusion in a case where printing pressureless than normal is applied.

FIG. 33 is an external view of protrusions to describe an example ofcorrecting a relief engraving shape (tip volume) for printing of aprotruded thin line in accordance with distribution of printingpressure, and includes: a portion (a) that is a perspective view thatshows an appearance of a protrusion for printing of a protruded thinline; a portion (b) that is a cross-sectional view of a protrusion in acase where printing pressure more than normal is applied; a portion (c)that is a cross-sectional view of a protrusion in a case where normalprinting pressure is applied; and a portion (d) that is across-sectional view of a protrusion in a case where printing pressureless than normal is applied.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present invention will be described with reference tothe accompanying drawings. Hereinafter, an example in which the presentinvention is applied to “flexographic printing” will be described, butthe present invention is not limited to this. The present invention iswidely applicable to a printing technique using a printing plate onwhich a relief is formed.

FIG. 1 shows an example of a configuration of a main section of aflexographic printing press 10. FIG. 2 is an enlarged view of a contactportion between a flexographic printing plate 1 and a printing medium 3during printing.

The flexographic printing press (printing unit) 10 includes theflexographic printing plate 1, a plate cylinder 4 to which theflexographic printing plate 1 is attached through a cushion tape 2 suchas a double-sided tape, an anilox roller 8 to which ink is supplied by adoctor chamber 6, and an impression cylinder 9 that is provided so as toface the plate cylinder 4.

Ink is transferred from the anilox roller 8 to an apex (printing face)of a relief 50 of the flexographic printing plate 1. Then, while theprinting medium 3 passes through a nip between the plate cylinder 4 towhich the flexographic printing plate 1 is attached and the impressioncylinder 9, the flexographic printing plate 1 (the apex of the relief50) is pressed on the printing medium 3 to allow ink attached to theapex of the relief of the flexographic printing plate 1 to betransferred to the printing medium 3, so that a desired image is printedand formed on the printing medium 3.

FIG. 3 is a plan view showing an example of a laser engraving machine 20that forms the relief 50 on the flexographic printing plate 1.

The laser engraving machine 20 includes a drum 22, and an exposure head28 for applying exposure engraving to a flexographic plate (printingplate) F held on the drum 22. The exposure head 28 is mounted on a stage30 to be movable by a focus position change mechanism 32 and anintermittent feed mechanism 38.

The focus position change mechanism 32 includes a motor 34 and a ballscrew 36 for allowing the exposure head 28 to move back and forth withrespect to the drum 22 to which the flexographic plate F is attached.The motor 34 and the ball screw 36 control movement of the exposure head28 in a main scanning direction to adjust a focus position in exposureengraving processing.

The intermittent feed mechanism 38 includes a ball screw 40, and asub-scanning motor 42 that rotates the ball screw 40. The ball screw 40and the sub-scanning motor 42 control movement of the exposure head 28(stage 30) in a sub-scanning direction, so that the exposure head 28 isintermittently fed in a direction of an axis 24 of the drum 22 (thesub-scanning direction). The flexographic plate F attached on the drum22 is held by a chuck member 26 to fix a holding position of theflexographic plate F on the drum 22. The position at which theflexographic plate F is held by the chuck member 26 is within an areawhere the exposure head 28 does not perform exposure.

The flexographic plate F is irradiated with a laser beam from theexposure head 28 while the drum 22 is rotated, so that the relief 50desired is formed on a surface of the flexographic plate F. When thechuck member 26 passes through in front of the exposure head 28 withrotation of the drum 22, the exposure head 28 (stage 30) isintermittently fed in the sub-scanning direction, and then laserengraving is applied to a subsequent line.

Such “feeding of the flexographic plate F in the main scanning directionwith rotation of the drum 22” and “intermittent feeding of the exposurehead 28 in the sub-scanning direction” are combined with each other tocontrol an exposure scan position. In addition, intensity of a laserbeam based on exposure data (depth data) for each exposure scan positionand ON/OFF of the laser beam are controlled so that the relief 50 in adesired shape is formed on the flexographic plate F by the laserengraving. As a result, the flexographic printing plate 1 to be used inflexographic printing (refer to FIGS. 1 and 2) is formed.

(Relationship Between Distribution of Printing Pressure and PrintingResult)

The flexographic printing plate 1 (particularly the relief 50) is formedof a soft member rich in elasticity to be deformed in accordance withprinting pressure. Thus, an amount of deformation of the relief 50varies depending on the amplitude of printing pressure applied, so thata printed image formed on the printing medium 3 also varies. Theprinting pressure applied to the flexographic printing plate 1 varieswith not only a kind of the relief 50 (such as a white space, a dot, aprotruded thin line, a solid fill) at a position of interest, but alsoby a kind of the relief 50 in the periphery of the position of interest.

FIG. 4 is a plan view showing an example of a relief formed in a part ofthe flexographic printing plate 1. The relief 50 of the flexographicprinting plate 1 shown in FIG. 4 is based on 1-bit image data.

In the flexographic printing plate 1 shown in FIG. 4, there are a “whitespace area” for printing a white space (a left side of FIG. 4) and a“solid fill area” for printing a solid fill (a right side of FIG. 4),across a “dot area” where the relief 50 for printing dots with uniformdot density (area ratio) is formed. In a case where the flexographicprinting plate 1 includes such plurality of kinds of area (relief 50),printing pressure applied to each of the areas during printing variesdepending on a kind of adjacent area. That is, relatively high printingpressure is to be received on a side adjacent to the white space area(refer to a “high printing pressure area” of FIG. 4), in the dot area,and on the other hand, relatively low printing pressure is received on aside adjacent to the solid fill area (refer to a “low printing pressurearea” of FIG. 4), in the dot area.

FIG. 5 shows an example of a relationship between areas (positions inthe direction of an arrow A of FIG. 4) of the flexographic printingplate 1 shown in FIG. 4 and an amount of depression during printing.FIG. 6 shows an example of a relationship between the areas (positionsin the direction of an arrow A of FIG. 4) of the flexographic printingplate 1 shown in FIG. 4 and printing pressure during printing. Inaddition, FIGS. 5 and 6 show the relationship in a case where the sameload is uniformly applied to each of the “white space area”, the “dotarea”, and the “solid fill area” of the flexographic printing plate 1shown in FIG. 4. In addition, FIGS. 5 and 6 respectively show changes in“the amount of depression” and the “printing pressure”, along a sectionline shown in each of displays of the “upper portion”, the “centralportion”, and the “lower portion”, of FIG. 4.

In the flexographic printing plate 1, in the “white space area” that isnot brought into contact with a printing medium, movement of the platein a depression direction is not obstructed during printing. As aresult, the amount of depression during printing tends to increase ascompared with the “dot area” and the “solid fill area”, which arebrought into contact with the printing medium, so that the movement ofthe plate in the depression direction is obstructed (refer to FIG. 5).In addition, since the “white space area” is not brought into contactwith the printing medium, printing pressure occurring between the “whitespace area” and the printing medium basically becomes zero (refer toFIG. 6).

Meanwhile, the “solid fill area” in the flexographic printing plate 1 isgenerally brought into contact with the printing medium, so thatdepression movement of the plate is obstructed during printing. As aresult, the amount of depression itself during printing decreases ascompared with the “white space area” and the “dot area” (refer to FIG.5). In addition, as a ratio of contact area with the printing mediumincreases, pressure per unit area decreases. Thus, if the same load isapplied, printing pressure in the “solid fill area” of the flexographicprinting plate 1 whose whole area is brought into contact with theprinting medium is lower than that in the “dot area” that is partiallybrought into contact with the printing medium (refer to FIG. 6).

Further, the “dot area” in the flexographic printing plate 1 ispartially brought into contact with the printing medium, so that thedepression movement of the plate is obstructed during printing. As aresult, the amount of depression during printing decreases as comparedwith the “white space area”, but increases as compared with the “solidfill area” (refer to FIG. 5). The printing pressure in the “dot area” ofthe flexographic printing plate 1 during printing is more than that inthe “white space area” that is not brought into contact with theprinting medium, as well as is more than that in the “solid fill area”with a high contact area ratio with the printing medium.

As above, the amount of depression and the printing pressure of theflexographic printing plate 1 during printing are affected bycharacteristics of each of the areas themselves (the relief 50 andcontact area), and are further affected by kinds and characteristics ofadjacent area.

For example, on a side of the “dot area” near the “white space area” inthe example shown in FIG. 4, relatively high printing pressure isapplied due to an effect of the amount of depression in the white spacearea, so that the amount of depression is also relatively increased onthe side (refer to the “high printing pressure area” of FIGS. 5 and 6).Meanwhile, on a side of the “dot area” near the “solid fill area”,relatively low printing pressure is applied due to an effect of theamount of depression in the “solid fill area”, so that the amount ofdepression is also relatively reduced on the side (refer to the “lowprinting pressure area” of FIGS. 5 and 6). As above, a relief (smalldot) in the dot area where a level of deformation varies with printingpressure is affected by a kind of relief in the periphery of the dotarea, so that a printing condition may change depending of a position.

FIG. 7 is a plan view of the printing medium 3 that shows an actualprinted image in a case where normal printing is performed with theflexographic printing plate shown in FIG. 4, and that particularly showsa printed image (the printing medium 3) obtained on the assumption thatplate thickness is uniform throughout the flexographic printing plate 1.

In actual printing, deviation of printing pressure occurs due to aneffect of a kind of relief in peripheral areas (refer to FIG. 6), sothat a printing condition on the printing medium 3 is affected by suchdeviation of the printing pressure. Thus, in the actual printing, asshown in FIG. 7, an uneven printing condition occurs in the “highprinting pressure area” in the dot area adjacent to the white spacearea, and the “low printing pressure area” therein adjacent to the solidfill area.

In addition, an amount of depression and printing pressure of theflexographic printing plate 1 during image printing is also affected byplate thickness that the flexographic printing plate 1 originally has.That is, the “amount of depression” and the “printing pressure” in aportion with a large plate thickness in the flexographic printing plate1 become larger than those in a portion with a small plate thicknesstherein.

FIG. 8 shows distribution of plate thickness of the flexographicprinting plate 1 in accordance with FIGS. 4 to 6. In FIG. 8, a deeperportion shows a smaller plate thickness, and a portion closer to white(blank) shows a larger thickness. In the examples shown in FIGS. 4 to 6,and 8, the plate thickness decreases in the order of an “upper portion”,a “central portion”, and a “lower portion”, and a value of each of “theamount of depression” and the “printing pressure” decreases in the orderof the “upper portion”, the “central portion”, and the “lower portion”.That is, since a plate thickness of the upper portion of the plate isrelatively large and a plate thickness of the lower portion of the plateis relatively small, printing pressure of the upper portion of the platebecomes relatively large and printing pressure of the lower portion ofthe plate becomes relatively small. In this way, the plate thicknessaffects amplitude of the printing pressure, whereby in a dot area and aprotruded thin line area, a printed image of a portion with a largeplate thickness (refer to the “upper portion” of each of FIGS. 4 and 8)becomes dark (thick), and a printed image of a portion with a smallplate thickness (refer to the “lower portion” of each of FIGS. 4 and 8)becomes light (thin).

FIG. 9 is a plan view of the printing medium 3 showing an ideal printedimage targeted when ideal printing is performed with the flexographicprinting plate 1 shown in FIG. 4. FIG. 10 is a plan view of the printingmedium 3 showing an actual printed image when normal printing isperformed with the flexographic printing plate 1 shown in FIG. 4.

As shown in FIG. 9, in a case where printing is performed in idealconditions, printing is performed so that the relief 50 of theflexographic printing plate 1 is properly reflected. As a result, aboundary among the “white space area”, the “dot area”, and the “solidfill area” is also made clear, so that a printing condition in each ofthe areas becomes uniform.

However, actual printing is affected by a kind of relief in a peripheralarea (refer to FIG. 7) and distribution of plate thickness (distributionof plate height) of the flexographic printing plate 1 (flexographicplate F) (refer to FIG. 8), as shown in FIG. 10. That is, since extentof deformation of a small dot in a dot area varies depending on a kindof relief in a peripheral area and height of a plate surface varies witha variation in plate thickness, printing conditions on the printingmedium 3 is affected by deviation of printing pressure. As above, sincea printing condition of an area of interest depends on distribution ofengraving shape (a kind of relief) in peripheral areas and distributionof plate thickness, a printing result intended by a user may not beobtained in flexographic printing by a normal method.

The inventor of the present invention has focused attention on this kindof relationship between distribution of printing pressure and a printingcondition, and has newly found out a technique capable of favorablyreproducing an image on a printing medium (printing medium) bydetermining a relief (engraving shape) of a printing plate inconsideration of deformation of a printing plate in accordance withdistribution of printing pressure. That is, image data to be printed anddistribution of plate thickness are analyzed so that distribution ofprinting pressure to be applied to the flexographic printing plate 1 isestimated, and then an engraving shape is determined (corrected) inconsideration of deformation of the flexographic printing plate 1 basedon the distribution of printing pressure estimated. As a result, it ispossible to accurately print and reproduce a desired image on a printingmedium.

Hereinafter, an example of a printing press that corrects an engravingshape on the basis of such distribution of printing pressure will bedescribed.

(Example of Configuration of Printing Press)

FIG. 11 is a block diagram showing a configuration of a flexographicprinting system (printing letterpress creation system) 60 in accordancewith one embodiment of the present invention.

The flexographic printing system 60 includes a raster image processor(RIP) device 61 and the printing plate manufacturing apparatus 62, andthe RIP device 61 and the printing plate manufacturing apparatus 62constitute a platemaking device (platemaking method) that forms a relief50 (relief pattern) based on image data (relief pattern data) on theflexographic plate F (flexographic printing plate 1).

The RIP device 61 includes an RIP processing unit 66, a screeningprocessing unit (binary image data creation unit) 68, and an exposureamount data creation unit 70.

The RIP processing unit 66 expands page description language data, suchas portable document format (PDF) data and PostScript (PS; a registeredtrademark) data, expressing a vector image of a camera-ready copy editedby using a computer or the like, into raster image data.

Each pixel data constituting the raster image data can have 8-bit foreach channel in four channels of CMYK, or 256 (0 to 255) gradations, asa gradation value. This kind of gradation can be converted into acorresponding dot area ratio (dot density). For example, in a case whereeach pixel data has values of from 0 to 100, if image data has a valueof 100, a solid portion may be formed, and if the image data has a valueof 0, a dot protrusion (a dot printing protrusion, or simply aprotrusion) may not be formed.

The screening processing unit 68 performs a screening of the rasterimage data under a condition such as a predesignated dot (such anAM-dot, and an FM-dot), an angle, and a screen ruling to convert theraster image data into binary image data. For example, if a screenruling is set at 175 lines per inch, and gradation that can be expressedby one dot is set at 256(=16×16) gradations, the screening processingunit 68 can create binary bitmap data with a resolution of 2800(=175×16) dpi.

The exposure amount data creation unit 70 converts the binary image datainto exposure amount data that can be expressed by 16-bit (65536gradations) or the like. Details of the exposure amount data creationunit 70 will be described later (refer to FIG. 12).

Meanwhile, the printing plate manufacturing apparatus 62 includes acomputer-to-plate (CTP) drawing machine 72 of an engraving type, and theCTP drawing machine 72 includes the laser engraving machine 20 (refer toFIG. 3). In the printing plate manufacturing apparatus 62, laserengraving processing by the CTP drawing machine 72 is applied to aflexographic plate (elastic material such as synthetic resin, andrubber) on the basis of exposure amount data supplied from the RIPdevice 61 (exposure amount data creation unit 70), so that theflexographic printing plate 1 on which the relief 50 reflecting an imageto be printed is formed is engraved and manufactured.

The flexographic printing plate 1 manufactured as above is used in theflexographic printing press 10 (refer to FIGS. 1 and 2) provided in asubsequent stage to be used for printing a desired image on the printingmedium 3 by transfer printing.

FIG. 12 is a functional block diagram showing an example of aconfiguration of the exposure amount data creation unit 70 of FIG. 11.

The exposure amount data creation unit 70 includes the protrusion heightdata conversion unit 74, the engraving shape data conversion unit 76, aplate thickness distribution acquisition unit 77, the engraving shapedata correction unit 78, and the exposure amount data converter 80.

The protrusion height data conversion unit 74 converts binary image datafrom the screening processing unit 68 into protrusion height dataindicating two-dimensional distribution of height of the relief 50(height of a protrusion).

The engraving shape data conversion unit 76 converts the protrusionheight data supplied from the protrusion height data conversion unit 74into engraving shape data (relief pattern data) with higher resolution.The engraving shape data is acquired by applying two-dimensionalinterpolation to the protrusion height data to reproduce athree-dimensional shape of a protrusion, and may be set as depth dataindicating a distance in a depth direction of the flexographic plate F.

As above, in the present example, the protrusion height data conversionunit 74 and the engraving shape data conversion unit 76 constitute “arelief calculation unit that calculates relief pattern data on the basisof image data”.

The plate thickness distribution acquisition unit 77 acquiresdistribution data of plate thickness showing distribution of platethickness of the flexographic plate F (flexographic printing plate 1).In the example shown in FIG. 12, a plate thickness distributionmeasuring device 46 provided separately from the exposure amount datacreation unit 70 (RIP device 61) measures thickness (distribution ofplate thickness) of the flexographic plate F of an object of reliefengraving, and then a plate thickness distribution storage unit 48stores a result of the measurement. The plate thickness distributionacquisition unit 77 reads out thickness measurements (distribution dataof plate thickness) of the flexographic plate F, stored in the platethickness distribution storage unit 48, and supplies the thicknessmeasurements to the engraving shape data correction unit 78.

The engraving shape data correction unit 78 corrects engraving shapedata (relief pattern data) on the basis of distribution of printingpressure of the flexographic printing plate 1 (engraving shape data, anddistribution data of plate thickness). Details of the engraving shapedata correction unit 78 will be described later (refer to FIG. 13).

The exposure amount data converter 80 converts the engraving shape data(relief pattern data) corrected by the engraving shape data correctionunit 78 into exposure amount data corresponding to an amount of exposurewith respect to the flexographic plate F. In the present example, theexposure amount data converter 80 (exposure amount data creation unit70) is provided as a part of the RIP device 61 (refer to FIG. 11), butmay be provided on a printing plate manufacturing apparatus 62 side.

In this way, the exposure amount data is calculated from correctionengraving shape data (relief pattern data), and the printing platemanufacturing apparatus 62 (refer to FIG. 11) forms the relief 50 on theflexographic plate F (flexographic printing plate 1) on the basis of theexposure amount data calculated.

Data correction based on distribution of printing pressure of theflexographic printing plate 1 may be performed by a variety of methods,and an amount of data correction calculated on the basis of thedistribution of printing pressure may be reflected in the engravingshape data or the exposure amount data. If the amount of data correctionis reflected in the engraving shape data, the engraving shape dataincluding the amount of correction is converted into the exposure amountdata, whereby exposure processing is performed by using the exposureamount data converted. On the other hand, if the amount of datacorrection is reflected in the exposure amount data, “the exposureamount data based on the engraving shape data (the amount of datacorrection is not reflected)” and “the exposure amount data based on theamount of data correction itself” are calculated, whereby “the exposureamount data reflecting the amount of data correction” is calculated fromboth data pieces. In an example shown in FIG. 13 below, a case where theamount of data correction is reflected in the engraving shape data willbe described.

FIG. 13 is a functional block diagram showing an example of aconfiguration of the engraving shape data correction unit 78 of FIG. 12.

The engraving shape data correction unit 78 includes a printing pressuredistribution estimation unit 82, a correction amount calculation unit84, and a data correction unit 86.

The printing pressure distribution estimation unit 82 estimatesdistribution of printing pressure of the flexographic printing plate 1pressed on the printing medium 3 during printing, on the basis ofengraving shape data (image data) and distribution data of platethickness. In addition, the printing pressure distribution estimationunit 82 may estimate the distribution of printing pressure on the basisof not only image data before being converted into the engraving shapedata, but also the engraving shape data. In a case where thedistribution of printing pressure is calculated more accurately or arelief shape cannot be formed by engraving as shown by a 1-bit image dueto characteristics of an engraving device (printing plate manufacturingapparatus 62), it is preferable that the distribution of printingpressure is estimated on the basis of engraving shape data showing ashape to be actually engraved.

The correction amount calculation unit 84 calculates the amount ofcorrection of the engraving shape data (relief pattern data) on thebasis of the distribution of printing pressure estimated by the printingpressure distribution estimation unit 82. A specific example of thecalculation of the amount of correction will be described later (referto FIG. 17).

The data correction unit 86 corrects the engraving shape data (reliefpattern data) acquired by the engraving shape data conversion unit 76,on the basis of the amount of correction calculated by the correctionamount calculation unit 84.

FIG. 14 is a flow chart that shows an outline of a flow of processing inthe engraving shape data correction unit 78 and the exposure amount dataconverter 80, and that shows an example of estimating distribution ofprinting pressure on the basis of image data before being converted intothe engraving shape data and the distribution data of plate thickness.In the example shown in FIG. 14, the distribution of printing pressureis calculated on the basis of an image and distribution of plate height,and an engraving shape is corrected in accordance with the distributionof printing pressure. Further, since an exposure beam diameter isdifferent depending on plate height, exposure correction and exposureconversion are performed so as to be able to acquire an engraving shapetargeted, whereby it is possible to manufacture the relief 50 in anengraving shape by previously considering the distribution of printingpressure.

In the present example, the printing pressure distribution estimationunit 82 (refer to FIG. 13) calculates the distribution of printingpressure of the flexographic printing plate 1 (S10 of FIG. 14) on thebasis of the image data before being converted into the engraving shapedata (refer to an example of 1-bit image data shown in FIG. 23 describedlater) and the distribution data of plate thickness.

Then, the correction amount calculation unit 84 calculates an amount ofcorrection of the engraving shape data from a calculation result of thedistribution of printing pressure, and then the data correction unit 86corrects the engraving shape data on the basis of the amount ofcorrection calculated (S11). Subsequently, the exposure amount dataconverter 80 applies exposure correction based on the distribution dataof plate thickness to the engraving shape data (S12), and furtherconverts the engraving shape data after the exposure correction intoexposure amount data (S13). The amount of data correction based on thedistribution of printing pressure may be reflected in either of databefore being converted into the exposure amount data or of data afterconversion. In addition, as described above, the engraving shape databefore being converted into the exposure amount data may be corrected onthe basis of an amount of calculation correction, or the exposure amountdata after the conversion may be corrected on the basis of the amount ofcalculation correction.

FIG. 15 shows a laser diameter at the time of laser exposure of thelaser engraving machine 20. A laser L to be used in exposure processingof forming the relief 50 on the flexographic plate F (flexographicprinting plate 1) changes in a beam diameter depending on its directionof travel (plate thickness direction) C.

That is, the laser L has a beam diameter d₀ at a focus position f₀ thatbecomes minimum, and with respect to the focus position f₀, a beamdiameter increases in accordance with a distance from the focus positionf₀ (relative height). For example, in an example shown in FIG. 15, inthe plate thickness direction C, “a beam diameter d_(p) at a focusposition f_(p) (a distance from the reference focus position f₀ isdesignated as T_(p))” and “a beam diameter d_(q) at the focus positionf_(q) (a distance from the reference focus position f₀ is designated asT_(q))” have a relationship of “d_(q)>d_(p)” is a case of “T_(q)>T_(p)”.In addition, the beam diameter of the laser L has symmetry with respectto the focus position f₀ in the direction of travel (plate thicknessdirection) C. Thus, with respect to focus positions f_(m) and f_(n)positioned on an opposite side to the focus positions f_(p) and f_(q)described above across the reference focus position f₀, if a distanceT_(m) from the reference focus position f₀ to the focus position f_(m)satisfies a relationship of “T_(m)=T_(p)”, a beam diameter d_(m) at thefocus position f_(m) satisfies a relationship of “d_(m)=d_(p)”.Likewise, if a distance T_(n) from the reference focus position f₀ tothe focus position f_(n) satisfies a relationship of “T_(n)>T_(m)”, abeam diameter d_(n) at the focus position f_(n) satisfies a relationshipof “d_(n)>d_(m)”.

Since a beam diameter of the laser L is an element that affects anirradiation range and irradiation intensity of the laser L, exposureprocessing using the laser L has specific exposure characteristics (suchas a beam diameter, and irradiation intensity) in a thickness directionof the flexographic plate F (flexographic printing plate 1). Thus, it ispreferable to consider this kind of exposure characteristics of thelaser L in the exposure processing. Particularly, if thickness of theflexographic plate F (flexographic printing plate 1) is not uniform, itis possible to improve engraving accuracy of the relief 50 byconsidering exposure characteristics of the laser L in the platethickness direction. As a result, the exposure amount data converter 80derives the exposure characteristics of the laser L in the platethickness direction from the distribution data of plate thickness, andthe exposure characteristics are reflected in the engraving shape dataand the exposure amount data (S12 of FIG. 14).

The engraving shape data to which the “correction of distribution ofprinting pressure” (S11) and the “exposure correction” (S12) are appliedas described above is converted into the exposure amount data by theexposure amount data converter 80 (S13), and then the exposure amountdata is transmitted to the printing plate manufacturing apparatus 62(refer to FIG. 11). The “exposure correction based on the distributiondata of plate thickness (S12)” described above may be performed alongwith “conversion of the exposure amount data (S13)”. That is, correctionin which exposure characteristics are considered so that a manufacturingerror based on the exposure characteristics that vary with platethickness of the flexographic plate F is canceled may be applied in astage of engraving shape data, or in a stage of exposure amount data.

By a series of the processes (S10 to S13) described above, it ispossible to calculate the exposure amount data for accurately formingthe relief 50 with an engraving shape, in consideration of thedistribution of printing pressure, on the flexographic plate F(flexographic printing plate 1) by the exposure processing inconsideration of the exposure characteristics.

FIG. 16 is a flow chart that shows an outline of a flow of processing inthe engraving shape data conversion unit 76, the engraving shape datacorrection unit 78, and the exposure amount data converter 80, and thatshows an example of estimating distribution of printing pressure on thebasis of engraving shape data and distribution data of plate thickness.A description of a portion common to that of FIG. 14 will be omitted.

When the protrusion height data conversion unit 74 (refer to FIG. 12)acquires protrusion height data (relief pattern data), the engravingshape data conversion unit 76 calculates engraving shape data byconverting the protrusion height data (image data) (S20 of FIG. 16).

Then, the printing pressure distribution estimation unit 82 calculatesdistribution of printing pressure of the flexographic printing plate 1on the basis of the engraving shape data acquired and the distributiondata of plate thickness (S21). Subsequently, the correction amountcalculation unit 84 and the data correction unit 86 calculate the amountof correction of the engraving shape data and correct the engravingshape data on the basis of the distribution of printing pressure (S22),and then the exposure amount data converter 80 (refer to FIG. 12)performs exposure correction based on the distribution data of platethickness (S23) and conversion into exposure amount data (S24).

Next, an example of calculation of the amount of correction of engravingshape data, based on distribution of printing pressure of theflexographic printing plate 1, will be described.

FIG. 17 is a flow chart that describes an example of a process ofcalculating a pressed amount (distribution of printing pressure) on thebasis of image data (engraving shape data) and plate thicknessdistribution to calculate the amount of correction based on the pressedamount (distribution of printing pressure). Although each processing inthe flow of FIG. 17 is mainly performed by the correction amountcalculation unit 84 of the engraving shape data correction unit 78(refer to FIG. 13), another unit may perform a part of the processing ifnecessary.

Range affected by distribution of printing pressure of the flexographicprinting plate 1 varies with “plate hardness (Shore A) of theflexographic printing plate 1” and “viscoelasticity of the flexographicprinting plate 1”. Thus, it is desirable that a size of a region ofinterest (ROI) that is a “range of distribution of printing pressure(predetermined range) serving as a basis of calculation of the amount ofcorrection of engraving shape data” is determined on the basis of theplate hardness and the viscoelasticity of the flexographic printingplate 1. Accordingly, first, the ROI (range of distribution of printingpressure) is determined on the basis of the plate hardness and theviscoelasticity of the flexographic printing plate 1 that are previouslyacquired and stored in a memory and the like (S30 of FIG. 17).

FIG. 18 shows an example of an image to describe the ROI. The ROI iscomposed of an area of the predetermined range by centering a positionof interest (a pixel of interest) in an image, and an amount ofcorrection of relief engraving (engraving shape data) at the position ofinterest is calculated on the basis of distribution of printing pressurein the ROI. Thus, the ROI is set for each position in the image, andwhile the position of interest is sequentially changed in the image,“calculation of the amount of correction of relief engraving at theposition of interest based on distribution of printing pressure in theROI” described later is performed. For example, in a case where theplate hardness (Shore A) of the flexographic printing plate 1 is 79° andthe viscoelasticity is approximately 15 MPa as well as a circular ROIsuch as shown in FIG. 18 is applied, a size (diameter) of the ROI may beset at a range of from 500 μm to 3000 μm. Although a circular ROI bycentering a position of interest is set in the example shown in FIG. 18,a size and a shape of the ROI is not particularly limited.

Next, a ground area ratio (contact area ratio) of the flexographicprinting plate 1 with respect to the printing medium 3 in a range of theROI is calculated (S31 of FIG. 17).

That is, a ratio (a ground area ratio in the ROI) R of “area (contactarea) of a relief portion that is to be brought into contact with theprinting medium 3 in the ROI during printing, and that corresponds to asupport of the flexographic printing plate 1 against the printing medium3” with respect to “the entire area of the ROI” is calculated. Forexample, if the entire range in the ROI is a white space area, theflexographic printing plate 1 (relief 50) and the printing medium 3 arenot brought into contact with each other, whereby the area ratio is 0%and the R is zero (R=0). Meanwhile, if the entire range in the ROI is asolid fill area, the flexographic printing plate 1 (relief 50) isbrought into contact with the printing medium 3 in the entire range ofthe ROI, whereby the area ratio is 100% and the R is 1 (R=1). Thus, asthe white space area increases in the ROI, the R becomes close to zero,and as the solid fill area increases in the ROI, the R becomes close to1.

Next, a kind of relief at a position of interest (a pixel of interest)is determined, and first, it is determined whether or not the positionof interest is an area corresponding to dots (S32 of FIG. 17). Thedetermination is performed for each of positions of interest (pixels ofinterest) on the basis of image data (engraving shape data).

If the position of interest is the area corresponding to dots (YES atS32), a pressed amount at the position of interest corresponding to anarea ratio of a dot area (ground area ratio, dot area ratio, and dotdensity) R is acquired (S33).

FIG. 19 shows an example of a correspondence relation between a groundarea ratio in an ROI and a pressed amount.

As shown in FIG. 19, in a case where the same load is applied, as theground area ratio in the ROI increases, the pressed amount decreases,and as the ground area ratio in the ROI decreases, the pressed amountincreases. It is because that as contact area decreases, force appliedper unit area (printing pressure) increases, whereby the pressed amountalso increases with the increase in printing pressure. This kind of“correspondence relation between a ground area ratio in an ROI and apressed amount” is previously measured and stored in a memory (notshown) and the like to be appropriately read out if necessary. Then, apressed amount at the position of interest, corresponding to the arearatio R of the dot area, is acquired on the basis of the “correspondencerelation between a ground area ratio in an ROI and a pressed amount”read out.

In this way, in the present example, a “pressed amount” associated with“distribution of printing pressure” is used as a parameter, and theparameter of a “pressed amount” is used to (indirectly) estimatedistribution of printing pressure of a printing plate pressed on aprinting medium on the basis of image data. Although “printing pressure(distribution of printing pressure)” may be used as a usage parameter,it is better to use the “pressed amount” as a parameter to facilitatecalculation processing from a point of view of performing correctionbased on distribution data of plate thickness described later.

The pressed amount at a position of interest acquired in this way iscorrected by data correction on the basis of height distribution(distribution of plate thickness) of the flexographic plate F(flexographic printing plate 1) (S34 of FIG. 17). That is, the pressedamount at a position of interest is corrected so that a variation inprinting pressure, caused by a variation in plate thickness of theflexographic plate F, is canceled. The distribution of plate thicknesscan be set with respect to height of the lowest position in a solid fillarea (reference height), or a contact position of the lightest portionin the solid fill area, on the basis of correspondence with an image. Asa result, data on a pressed amount at a position of interest iscorrected so that the pressed amount at the position of interestincreases if a relief tip position (relief contact position) at theposition of interest (a pixel of interest) is relatively high withrespect to the reference height, and so that the pressed amount at theposition of interest decreases if the relief tip position at theposition of interest is relatively low with respect to the referenceheight.

Then, the amount of correction of engraving shape data is acquired onthe basis of “data on a pressed amount at a position of interest”corrected (S35).

FIG. 20 shows an example of a correspondence relation between “a pressedamount at a position of interest (a pixel of interest)” and “the amountof correction of engraving shape data at the position of interest”. InFIG. 20, a “reference value” is equivalent to a pressed amountcorresponding to a predetermined normal printing pressure.

As shown in FIG. 20, as the pressed amount increases, the amount ofcorrection increases, and as the pressed amount decreases, the amount ofcorrection decreases. It is because that as the pressed amountincreases, force applied per unit area (printing pressure) alsoincreases to cause also an amount of deviation from an original printedimage to tend to increase with the increase in printing pressure. Thiskind of “correspondence relation between a pressed amount and an amountof data correction” is previously measured and stored in a memory (notshown) and the like to be appropriately read out if necessary. Then,there is acquired the amount of correction of engraving shape datacorresponding to the “data on a pressed amount at a position ofinterest” corrected on the basis of the “correspondence relation betweena pressed amount and an amount of data correction” read out.

In this way, although the pressed amount and the amount of datacorrection are calculated on the basis of image data and distributiondata of plate thickness, that way equivalent to a way in whichdistribution of printing pressure is estimated on the basis of the imagedata and the distribution data of plate thickness, and the amount ofcorrection of relief pattern data is calculated on the basis of thedistribution of printing pressure.

Since data showing “the correspondence relation between a ground arearatio in an ROI and a pressed amount” shown in FIG. 19, and data showing“the correspondence relation between a pressed amount at a position ofinterest (a pixel of interest) and the amount of data correction” shownin FIG. 20, vary depending on characteristics of the flexographic plateF, and engraving characteristics (relief forming characteristics) of thelaser engraving machine 20, each data is determined according to asystem to be used (the flexographic printing system 60). Thus, data on“a correspondence relation between a ground area ratio in an ROI and apressed amount” and data on “a correspondence relation between a pressedamount at a position of interest (a pixel of interest) and the amount ofdata correction”, previously acquired for each of kinds of reliefaccording to a usage system, are stored in a predetermined memory (notshown) or the like to be appropriately read out and used when “theamount of correction of engraving shape data” is calculated.

In addition, if a position of interest is a dot, it is desirable thatcharacteristics of “a correspondence relation between a ground arearatio in an ROI and a pressed amount” (refer to FIG. 19) andcharacteristics of “a correspondence relation between a pressed amountat a position of interest (a pixel of interest) and the amount of datacorrection” (refer to FIG. 20) are changed and determined in accordancewith a dot area ratio (dot density:dot percent). It is because that if adot has a high dot percent (particularly, a dot with a dot area ratio of50 percent or more), deformation of the relief 50 of the flexographicprinting plate 1 during printing is relatively small, and if a dot has alow dot percent, the deformation of the relief 50 of the flexographicprinting plate 1 during printing is relatively large.

In this way, “the amount of correction of engraving shape data” in acase where a position of interest is a dot is calculated. Meanwhile,also in a case where a position of interest is a protruded thin line,“the amount of correction of engraving shape data” is calculated in likemanner.

That is, if it is determined that a position of interest is not a dot(NO at S32 of FIG. 17) but an area corresponding to a protruded thinline (YES at S36), a pressed amount at a position of interestcorresponding to the area ratio (ground area ratio) R of a protrudedthin line area is acquired (S37, and refer to FIG. 19). Then, data on apressed amount at the position of interest is corrected on the basis ofthe distribution data of plate thickness of the flexographic plate F(S38), and the amount of correction of engraving shape data is acquiredon the basis of the “data on a pressed amount at the position ofinterest” corrected (S39, and refer to FIG. 20).

In this case, for the characteristics of “a correspondence relationbetween a ground area ratio in an ROI and a pressed amount” as well asthe characteristics of “a correspondence relation between a pressedamount at a position of interest (a pixel of interest) and the amount ofdata correction”, to be a basis of calculation of the amount ofcorrection of engraving shape data, characteristics in a case where aposition of interest is a protruded thin line are used, and aredifferent from characteristics in a case where a position of interest isa dot (refer to FIGS. 19 and 20).

Meanwhile, in a case where it is determined that a position of interestis not a protruded thin line (NO at S36), but an area corresponding to asolid fill (YES at S40), the amount of correction is not calculated, andalso correction of the engraving shape data by the data correction unit86 (refer to FIG. 13) is not performed and is skipped. It is becausethat in a solid fill area, the flexographic printing plate 1 and theprinting medium 3 are brought into contact with each other throughoutthe area so that correction of the engraving shape data is unnecessary.

Then, if it is determined that a position of interest is not any of adot, a protruded thin line, and a solid fill (NO at S40), a pressedamount at a position of interest corresponding to the area ratio (groundarea ratio) R of another area is acquired (S41, and refer to FIG. 19).Subsequently, data on a pressed amount at the position of interest iscorrected on the basis of the distribution data of plate thickness ofthe flexographic plate F (S42), and the amount of correction ofengraving shape data is acquired on the basis of the “data on a pressedamount at the position of interest” corrected (S43, and refer to FIG.20).

In this case, the characteristics of “a correspondence relation betweena ground area ratio in an ROI and a pressed amount” as well as thecharacteristics of “a correspondence relation between a pressed amountat a position of interest (a pixel of interest) and the amount of datacorrection”, to be a basis of calculation of the amount of correction ofengraving shape data, are different from characteristics in a case wherea position of interest is a dot (refer to FIGS. 19 and 20) and those ina case where a position of interest is a protruded thin line.

As with an ROI size, it is desirable that the characteristics of “acorrespondence relation between a ground area ratio in an ROI and apressed amount” as well as the characteristics of “a correspondencerelation between a pressed amount at a position of interest (a pixel ofinterest) and the amount of data correction”, to be used at the time ofcalculation of the amount of correction of engraving shape datadescribed above (refer to S30 to S43 of FIG. 17), are determined inaccordance with plate hardness and viscoelasticity of the flexographicprinting plate 1 (flexographic plate F) to be used, in any of caseswhere a position of interest is a dot, a protruded thin line, and otherthan those.

When the amount of correction of engraving shape data is determined asdescribed above, the data correction unit 86 of the engraving shape datacorrection unit 78 (refer to FIG. 13) corrects the engraving shape dataon the basis of the amount of correction determined.

In addition, the data correction unit 86 may be provided integrally withthe exposure amount data converter 80, “the amount of data correction”acquired on the basis of distribution of printing pressure may not bedirectly reflected in engraving shape data, but indirectly reflected inexposure amount data.

FIG. 21 is a table (conversion table) showing an example of an exposuretable to achieve shape correction, in which the “exposure table (an“exposure table 1” to an “exposure table 5” in a “dot”, a “protrudedthin line”, and “other than those”)” is associated with “the amount ofcorrection of engraving shape data (“the amount of correction 1” to “theamount of correction 5”)” and “a kind of relief of a position ofinterest (a pixel of interest)”.

In a case where the data correction unit 86 is provided integrally withthe exposure amount data converter 80, as shown in FIG. 21, for example,exposure amount data corresponding to each of “the amount of correctionof engraving shape data” determined (refer to “the amount of correction1” to “the amount of correction 5” of FIG. 21) may be predetermined foreach of cases of a “dot”, a “protruded thin line”, and “other thanthose” (the “exposure table 1” to the “exposure table 5”). In this case,the exposure amount data converter 80 is able to calculate exposureamount data reflecting the amount of correction for each of cases wherea position of interest is a dot, a protruded thin line, a solid fill,and other than those, on the basis of a conversion table such as shownin FIG. 21.

In this case, the exposure amount data converter 80 may perform alsoexposure correction based on the distribution data of plate thickness(refer to “S12” of FIG. 14, and “S23” of FIG. 16).

FIG. 22 is a table showing an exposure conversion table to achieve shapecorrection corresponding to a laser beam diameter. In FIG. 22, a “focusposition f₀” shows a position (reference focus position) where a beamdiameter becomes minimum (refer to FIG. 15), and “+” and “−” indicatepositions on opposite sides across the reference focus position f₀, andalso height is in terms of micro meter (μm). Thus, a “focus positionf₊₁” and a “focus position f₊₂”, and a “focus position f⁻¹” and a “focusposition f⁻²”, shown in FIG. 22, are respectively positioned on oppositesides across the reference focus position f₀ (refer to “f_(p)” and“f_(q)”, and “f_(m)” and “f_(n)”, of FIG. 15). In addition, the “focusposition f₊₁” and the “focus position f⁻¹” have the same distance fromthe reference focus position f₀, and also the “focus position f₊₂” andthe “focus position f⁻²” has the same distance therefrom.

As shown in FIG. 22, exposure amount data corresponding to relief heightmay be stored in a memory (not shown) or the like as an exposure table.The laser engraving machine 20 (refer to FIG. 3) adjusts a focusposition of the laser L with an autofocus mechanism so that apredetermined position of the flexographic plate F becomes a focusposition (“f₀” of FIG. 15). “Height” (focus position) shown in the tableof FIG. 22 shows a variation in plate height (plate thickness) withrespect to the reference focus position f₀ as a distance (relativeheight) with respect to the focus position f₀.

The exposure amount data converter 80 is capable of correcting exposureamount data (exposure correction) on the basis of the amount ofcorrection determined for each of positions of interest, with referenceto the exposure conversion table shown in FIG. 22. The exposure tablefor each of focus positions, such as shown in FIG. 22, is assigned toeach of the exposure tables (the “exposure table 1” to the “exposuretable 5”) determined by the amount of correction (“the amount ofcorrection 1” to “the amount of correction 5”) and a kind of relief(such as a “dot”, a “protruded thin line”, and “other than those”), suchas shown in FIG. 21. Thus, the exposure amount data converter 80determines a corresponding exposure table (FIG. 21) from a kind ofrelief (such as a “dot”, a “protruded thin line”, and “other thanthose”) at a position of interest (a pixel of interest) and the amountof data correction (“the amount of correction 1” to “the amount ofcorrection 5”) calculated. Meanwhile, the exposure amount data converter80 calculates a plate height (plate thickness) at a position of interestwith respect to the reference focus position f₀. Then, the exposureamount data converter 80 determines an exposure table corresponding tothe plate height (plate thickness) at the position of interest fromamong “exposure tables for respective focus positions, such as shown inFIG. 22”, assigned to the exposure table (FIG. 21) determined. Theexposure amount data is determined on the basis of the exposure tabledetermined in this way.

Then, the printing plate manufacturing apparatus 62 is able to form anappropriate relief of the flexographic printing plate 1 by engraving onthe basis of “the exposure amount data reflecting the amount ofcorrection” calculated in this way. In a conversion calculation processof exposure amount data based on an engraving algorithm corresponding toan engraving device (the printing plate manufacturing apparatus 62), the“exposure amount data reflecting the amount of correction” may becalculated by multiplying exposure amount data before correction(exposure amount data derived from engraving shape data beforecorrection) by a numeric value stored in a conversion table such asshown in FIGS. 21 and 22 (a correction reflecting value in an exposuretable).

(Example of Relief Correction)

The engraving shape data and the exposure amount data are corrected asdescribed above to enable relief correction in consideration ofdistribution of printing pressure and distribution of plate thickness.

FIG. 23 shows an example of image data (1-bit image data) before beingconverted into engraving shape data, and FIG. 24 shows an example ofengraving shape data that can be acquired from the image data of FIG.23. Each of FIGS. 23 and 24 shows a printed image 90 reproduced on theprinting medium 3 from image data and engraving shape data.

As described above, although distribution of printing pressure of theflexographic printing plate 1 is estimated on the basis of an area ratioof a portion within a predetermined range of the flexographic printingplate 1, the portion being brought into contact with the printing medium3, the distribution may be estimated on the basis of “image data beforebeing converted into engraving shape data”, such as shown in FIG. 23, oron the basis of “engraving shape data”, such as shown in FIG. 24.

Each of FIGS. 25 and 26 shows an example of “engraving shape data aftercorrection” that can be acquired by correcting the engraving shape datashown in FIG. 24 on the basis of distribution of printing pressure. Inaddition, each of FIGS. 25 and 26 shows the printed image 90 reproducedon the printing medium 3 by normal flexographic printing (transferprinting) on the basis of “engraving shape data after correction” byneglecting influence of distribution of printing pressure in theperiphery of a position of interest.

As compared with the engraving shape data (before correction) shown inFIG. 24, in the example shown in FIG. 25, “engraving shape data” iscorrected so that the printed image 90 is expanded as a whole, and inthe example shown in FIG. 26, the “engraving shape data” is corrected sothat the printed image 90 is reduced in size as a whole. Thus, forexample, if printing pressure applied to a position of interest issmaller than normal depending on a condition of the periphery thereof,engraving shape data is corrected to “engraving shape data that allowsthe printed image 90 to be expanded”, such as shown in FIG. 25, toenable the printed image 90 same as that in a case where normal printingpressure is applied to be reproduced on the printing medium 3 as aresult, even if applied printing pressure is smaller than normal.Meanwhile, if printing pressure applied to a position of interest islarger than normal depending on a condition of the periphery thereof,the engraving shape data is corrected to “engraving shape data thatallows the printed image 90 to be reduced in size”, such as shown inFIG. 26, to enable the printed image 90 same as that in a case wherenormal printing pressure is applied to be reproduced on the printingmedium 3 as a result, even if applied printing pressure is larger thannormal.

FIG. 27 is a perspective view that shows an appearance of an example ofthe relief 50 formed in a part of the flexographic printing plate 1, andthat shows an example of the relief 50 (protrusions 51) created on theflexographic printing plate 1 by engraving on the basis of engravingshape data to which correction in consideration of distribution ofprinting pressure is not applied. FIG. 28 is a perspective view thatshows an appearance of an example of the relief 50 formed in a part ofthe flexographic printing plate 1, and that shows an example of therelief 50 (protrusions 51) created on the flexographic printing plate 1by engraving on the basis of engraving shape data to which correction inconsideration of distribution of printing pressure is applied.

A relief pattern formed on the flexographic printing plate 1 includesthe plurality of protrusions 51, each of which has a base, and a tipthat is provided on the base to be pressed on the printing medium 3. Inflexographic printing, there are listed height (refer to “T_(A)” of FIG.27) of each of the protrusions 51, and a shape of the tip of each of theprotrusions 51, to be brought into contact with the printing medium 3(refer to a diameter “D_(A)” of FIG. 27), as an element thatsignificantly affects quality of the printed image 90 reproduced on theprinting medium 3.

Thus, it is preferable that the engraving shape data includes heightdata and shape data on the plurality of protrusions 51 included in therelief pattern, and that the amount of correction of engraving shapedata based on distribution of printing pressure relates to at least anyone of the height data and shape data on the protrusions 51.Particularly, it is preferable that the shape data on the protrusions 51includes at least shape data on the tip, and that the shape data on thetip includes data on a portion (face) of the tip that is brought intocontact with a printing medium during printing. In addition, it ispreferable that the height data on the plurality of protrusions relatesto at least any one of tip height, base height, entire height of the tipand base, and particularly to the entire height and the tip height.

Thus, it is preferable to adjust height (refer to “T_(B)(=T_(A)−ΔT)” ofFIG. 28) of the protrusions 51 (relief 50) formed on the flexographicprinting plate 1 and a shape of the tip (refer to a diameter “D_(B)” ofFIG. 28) by correction based on distribution of printing pressure.

FIG. 29 is an external view of the protrusions 51 to describe an exampleof correcting an engraving shape (tip shape) of a small dot in dots inaccordance with distribution of printing pressure, and includes: aportion (a) that shows the protrusion 51 in a case where printingpressure more than normal is applied; a portion (b) that shows theprotrusion 51 in a case where normal printing pressure is applied; and aportion (c) that shows the protrusion 51 in a case where printingpressure less than normal is applied.

Each of the protrusions 51 includes a base 52 in a truncated conicalshape, and a tip 53 in a cylindrical shape provided on the base 52, thetip 53 having a cross-sectional diameter that is the same as that of atop end of the base 52. In the example shown in FIG. 29, the “shape dataon the plurality of protrusions 51” in the engraving shape data includesat least the shape data on the tip 53, and the “shape data on the tip53” includes data on a portion of the tip 53 that is brought intocontact with the printing medium 3 during printing, and then the shape(diameter) of the tip 53 of the protrusion 51 is corrected and adjustedin accordance with distribution of printing pressure.

That is, in a case where printing pressure applied at a position ofinterest is within a normal range to be expected due to less influencefrom the periphery of the position of interest, a diameter of the“portion (ground portion) that is brought into contact with the printingmedium 3” of the tip 53 of the protrusion 51 is also set at a normalsize (refer to “D2” in the portion (b) of FIG. 29). Meanwhile, in a casewhere the printing pressure applied at the position of interest is morethan (excessively more than) a normal amplitude to be expected due toinfluence from the periphery of the position of interest, the diameterof the tip 53 of the protrusion 51 is reduced as compared with that atthe time of normal printing pressure (the portion (b) of FIG. 29) toreduce cross-sectional area of the tip (refer to “D1” in the portion (a)of FIG. 29). Accordingly, it is possible to perform predictioncorrection for reducing “expansion of the ground portion and the printedimage 90” that is may be caused by deformation of the protrusion 51 (tip53). In addition, in a case where the printing pressure applied at theposition of interest is less than (excessively less than) the normalamplitude to be expected due to influence from the periphery of theposition of interest, the diameter of the tip 53 of the protrusion 51 isincreased as compared with that at the time of normal printing pressure(the portion (b) of FIG. 29) to increase the cross-sectional area of thetip (refer to “D3” in the portion (c) of FIG. 29). Accordingly, it ispossible to perform prediction correction for reducing influence of“reduction of the ground portion and the printed image 90 in size” thatmay be caused by lack of deformation of the protrusion 51 (tip 53) dueto small amplitude of printing pressure.

FIG. 30 is an external view of the protrusions 51 (relief 50) todescribe an example of correcting an engraving shape (protrusion height)of a small dot in dots in accordance with distribution of printingpressure, and includes: a portion (a) that shows the protrusion 51 in acase where printing pressure more than normal is applied; a portion (b)that shows the protrusion 51 in a case where normal printing pressure isapplied; and a portion (c) that shows the protrusion 51 in a case whereprinting pressure less than normal is applied.

In the example shown in FIG. 29, although the “diameter of the tip 53 ofthe protrusion 51 (relief 50)” is adjusted to perform correction ofengraving shape data based on distribution of printing pressure, “heightof the protrusion 51” may be adjusted (to be low layer thickness or highlayer thickness) to perform such the correction. That is, it is possibleto prevent unintended deformation of the protrusion 51 during printingby adjusting height of a ground portion of the tip 53 of the protrusion51 to adjust the amplitude of printing pressure applied at a position ofinterest.

The adjustment of the “height of protrusion 51” described here meansthat relative relief height in a relief forming area of the flexographicprinting plate 1 is adjusted, and serves as adjustment of a relativeposition (relative height) with respect to a position of the apex ofrelief (height) in an area (refer to the “solid fill area” of FIG. 4)for printing a solid fill portion, for example.

Depending on characteristics of an engraving device, a ground face(minimum ground face) of the relief 50 (protrusions 51) to be used inprinting of a dot with a minimum diameter may be limited. Even in such acase, it is possible to reduce a small dot diameter of printing byadjusting the “height of the protrusion 51” to control a relativedistance with respect to the printing medium 3.

For example, in a case where printing pressure applied at a position ofinterest is within a normal range to be expected due to less influencefrom the periphery of the position of interest, the “height of theprotrusion 51” in the tip 53 of the protrusion 51 is also set at anormal height (refer to “T2” in the portion (b) of FIG. 30). Meanwhile,in a case where the printing pressure applied at the position ofinterest is more than (excessively more than) a normal amplitude to beexpected due to influence from the periphery of the position ofinterest, the “height of the protrusions 51” is reduced (refer to “T1”in the portion (a) of FIG. 30) as compared with that at the time ofnormal printing pressure (the portion (b) of FIG. 30). Accordingly, itis possible to perform prediction correction for reducing “expansion ofthe ground portion and the printed image 90” that may be caused bydeformation of the protrusion 51 (tip 53). In addition, in a case wherethe printing pressure applied at the position of interest is less than(excessively less than) the normal amplitude to be expected due to theinfluence from the periphery of the position of interest, the “height ofthe protrusions 51” is increased (refer to “T3” in the portion (c) ofFIG. 30) as compared with that at the time of normal printing pressure(the portion (b) of FIG. 30). Accordingly, it is possible to performprediction correction for reducing influence of “reduction of the groundportion and the printed image 90 in size” that may be caused by lack ofdeformation of the protrusion 51 (tip 53) due to small amplitude ofprinting pressure.

FIG. 31 is an external view of the protrusions 51 (relief 50) todescribe an example of correcting an engraving shape (protrusion tipvolume) of a small dot in dots in accordance with distribution ofprinting pressure, and includes: a portion (a) that shows the protrusion51 in a case where printing pressure more than normal is applied; aportion (b) that shows the protrusion 51 in a case where normal printingpressure is applied; and a portion (c) that shows the protrusion 51 in acase where printing pressure less than normal is applied.

In the example shown in each of FIGS. 29 and 30, although a size (tipdiameter or protrusions height) of the protrusion 51 (relief 50) in anone-dimensional direction is adjusted to correct engraving shape data onthe basis of distribution of printing pressure, the engraving shape datamay be corrected on the basis of the distribution of printing pressurefrom a three-dimensional viewpoint. That is, it is preferable that theengraving shape data directly or indirectly includes volume data on theplurality of protrusions 51 included in a relief pattern, and that theamount of correction of engraving shape data based on distribution ofprinting pressure relates to the volume data. Accordingly, it ispossible to prevent unintended deformation of the protrusion 51 duringprinting by controlling volume of the protrusion 51 (particularly,volume of the tip 53) to adjust the amplitude of printing pressureapplied at a position of interest. In addition, the “volume data on theprotrusions 51” described here may be indirect “volume data” shown bydata on a cross-sectional shape (such as a cross-sectional diameter) ofeach of the protrusions 51 (base 52 and tip 53) and height data on eachof the protrusions 51.

In the example shown in FIG. 31, each of the protrusions 51 includes thebase 52 in a truncated conical shape that is provided integrally withthe tip 53 in a truncated conical shape so that a bottom of the tip 53is positioned at an apex of the base 52, and a cross-sectional diameterof the apex of the base 52 does not coincide with a cross-sectionaldiameter of the bottom of the tip 53. Then, there is a relationship asfollows: “cross-sectional diameter of the apex of the base52”>“cross-sectional diameter of the bottom of the tip 53”. In this kindof structure, it is possible to control a small dot diameter of printingby adjusting the “volume of the tip 53 of the protrusion 51”.

For example, in a case where printing pressure applied at a position ofinterest is within a normal range to be expected due to less influencefrom the periphery of the position of interest, a diameter and height ofthe tip 53 is determined so that the volume of the tip 53 of theprotrusion 51 also becomes a normal size (refer to “D2” and “TH2” in theportion (b) of FIG. 31). Meanwhile, in a case where the printingpressure applied at the position of interest is more than (excessivelymore than) a normal amplitude to be expected due to influence from theperiphery of the position of interest, the diameter and height of thetip 53 is determined so that the volume of the tip 53 of the protrusion51 is reduced (refer to “D1” and “TH1” in the portion (a) of FIG. 31) ascompared with that at the time of normal printing pressure (the portion(b) of FIG. 31). Accordingly, it is possible to perform predictioncorrection for reducing “expansion of the ground portion and the printedimage 90” that may be caused by deformation of the protrusion 51 (tip53). In addition, in a case where the printing pressure applied at theposition of interest is less than (excessively less than) the normalamplitude to be expected due to influence from the periphery of theposition of interest, the diameter and height of the tip 53 isdetermined so that the volume of the tip 53 of the protrusion 51 isincreased (refer to “D3” and “TH3” in the portion (c) of FIG. 31) ascompared with that at the time of normal printing pressure (the portion(b) of FIG. 31). Accordingly, it is possible to perform predictioncorrection for reducing influence of “reduction of the ground portionand the printed image 90 in size” that may be caused by lack ofdeformation of the protrusion 51 (tip 53) due to small amplitude ofprinting pressure.

Volume of the base 52 may be adjusted in addition to the tip 53 of theprotrusion 51 (or instead of the tip 53 of the protrusion 51). That is,in order to reduce the influence from the periphery on printingpressure, a diameter and height of the base 52 may be determined so thatthe volume of the base 52 decreases if printing pressure more thannormal is applied, and so that the volume of the base 52 increases ifthe printing pressure less than normal is applied (refer to “DB1” to“DB3”, and “TH1” to “TH3”, in portions (a) to (c) of FIG. 31). However,since the volume of the tip 53 usually exerts more influence on printingpressure than does the volume of the base 52, it is better to controlthe volume (a diameter and height) of the tip 53 on a priority basis inmany cases.

In addition, an engraving shape (engraving shape data) of the relief 50(protrusions 51) for dots of the flexographic printing plate 1 may beadjusted by a technique other than the above, and in combination withthe techniques shown in FIGS. 29 to 31 described above, a diameter andheight of the tip 53 of the protrusion 51, a diameter and height of thebase 52, a size ratio (volume ratio) between the tip 53 and the base 52,and the like, may be appropriately adjusted.

Although FIGS. 29 to 31 above described correction of an engraving shapefor dot printing, another correction of an engraving shape may be alsoperformed in like manner.

FIG. 32 is an external view of the protrusions 51 to describe an exampleof correcting a relief engraving shape (tip shape) for printing of aprotruded thin line in accordance with distribution of printingpressure, and includes: a portion (a) that is a perspective view of theprotrusion 51 for printing of a protruded thin line; a portion (b) thatis a cross-sectional view of the protrusion 51 in a case where printingpressure more than normal is applied; a portion (c) that is across-sectional view of the protrusion 51 in a case where normalprinting pressure is applied; and a portion (d) that is across-sectional view of the protrusion 51 in a case where printingpressure less than normal is applied.

The protrusion 51 for printing of a protruded thin line of the presentexample includes the base 52 and the tip 53 provided on a top face ofthe base 52. The base 52 has a quadrangular prism shape with a side facein a trapezoidal shape, and the tip 53 has a quadrangular prism shapewith a side face in a rectangular shape.

For example, in a case where printing pressure applied at a position ofinterest is within a normal range to be expected due to less influencefrom the periphery of the position of interest, a size (width) of an“apex (ground portion) that is brought into contact with the printingmedium 3” of the tip 53 of the protrusion 51 is also set at a normalsize (refer to “D2” in the portion (c) of FIG. 32). Meanwhile, in a casewhere the printing pressure applied at the position of interest is morethan (excessively more than) a normal amplitude to be expected due toinfluence from the periphery of the position of interest, the size(width) of the tip 53 of the protrusion 51 is reduced as compared withthat at the time of normal printing pressure (the portion (c) of FIG.32) to reduce cross-sectional area of the tip (refer to “D1” in theportion (b) of FIG. 32). Accordingly, it is possible to performprediction correction for reducing “expansion of the ground portion andthe printed image 90” that may be caused by deformation of theprotrusion 51 (tip 53). In addition, in a case where the printingpressure applied at the position of interest is less than (excessivelyless than) the normal amplitude to be expected due to influence from theperiphery of the position of interest, the size (width) of the tip 53 ofthe protrusion 51 is increased as compared with that at the time ofnormal printing pressure (the portion (c) of FIG. 32) to increase thecross-sectional area of the tip (refer to “D3” in the portion (d) ofFIG. 32). Accordingly, it is possible to perform prediction correctionfor reducing influence of “reduction of the ground portion and theprinted image 90 in size” that may be caused by lack of deformation ofthe protrusion 51 (tip 53) due to small amplitude of printing pressure.

In addition, engraving shape data may be corrected from athree-dimensional viewpoint, so that it is possible to preventunintended deformation of the protrusion 51 during printing bycontrolling volume of the protrusion 51 (particularly, volume of the tip53) to adjust the amplitude of printing pressure applied at a positionof interest.

FIG. 33 is an external view of the protrusions 51 (relief 50) todescribe an example of correcting a relief engraving shape (tip volume)for printing of a protruded thin line in accordance with distribution ofprinting pressure, and includes: a portion (a) that is a perspectiveview that shows an appearance of the protrusion 51 for printing of aprotruded thin line; a portion (b) that is a cross-sectional view of theprotrusion 51 in a case where printing pressure more than normal isapplied; a portion (c) that is a cross-sectional view of the protrusion51 in a case where normal printing pressure is applied; and a portion(d) that is a cross-sectional view of the protrusion 51 in a case whereprinting pressure less than normal is applied.

The base 52 of the protrusion 51 for printing of a protruded thin lineof the present example has a quadrangular prism shape with a side facein a trapezoidal shape as with the protrusions 51 of FIG. 32, and thetip 53 also has a quadrangular prism shape with a side face in atrapezoidal shape.

For example, in a case where printing pressure applied at a position ofinterest is within a normal range to be expected due to less influencefrom the periphery of the position of interest, a size (width) of an“apex (ground portion) that is brought into contact with the printingmedium 3” of the tip 53 of the protrusion 51 is also set at a normalsize (refer to “D2” in the portion (c) of FIG. 33) so that volume of thetip 53 of the protrusion 51 also becomes normal. Meanwhile, in a casewhere the printing pressure applied at the position of interest is morethan (excessively more than) a normal amplitude to be expected due toinfluence from the periphery of the position of interest, a size (width)of a ground portion that is brought into contact with the printingmedium 3, of the tip 53, is determined so that the volume of the tip 53of the protrusion 51 is reduced (refer to “D1” in the portion (b) ofFIG. 33) as compared with that at the time of normal printing pressure(the portion (c) of FIG. 32). Accordingly, it is possible to performprediction correction for reducing “expansion of the ground portion andthe printed image 90” that may be caused by deformation of theprotrusion 51 (tip 53). In addition, in a case where the printingpressure applied at the position of interest is less than (excessivelyless than) the normal amplitude to be expected due to influence from theperiphery of the position of interest, a size (width) of the groundportion that is brought into contact with the printing medium 3, of thetip 53, is determined so that the volume of the tip 53 of the protrusion51 is increased (refer to “D3” in the portion (d) of FIG. 32) ascompared with that at the time of normal printing pressure (the portion(c) of FIG. 32). Accordingly, it is possible to perform predictioncorrection for reducing influence of “reduction of the ground portionand the printed image 90 in size” that may be caused by lack ofdeformation of the protrusion 51 (tip 53) due to small amplitude ofprinting pressure.

In addition, an engraving shape (engraving shape data) of the relief 50(protrusions 51) for a protruded thin line of the flexographic printingplate 1 may be adjusted by a technique other than the above, and incombination with the techniques shown in FIGS. 32 to 33 described above,a width and height of the tip 53 of the protrusion 51, a width andheight of the base 52, a size ratio (volume ratio) between the tip 53and the base 52, and the like, may be appropriately adjusted.

The present invention is not limited to the embodiments described above,and therefore it is needless to say that a variety of modifications arepossible within a range without departing from the spirit of the presentinvention.

What is claimed is:
 1. A platemaking method of forming relief based onrelief pattern data in a printing plate to be pressed on a printingmedium, the platemaking method comprising the steps of: calculatingrelief pattern data on the basis of image data; acquiring distributiondata of plate thickness showing distribution of plate thickness of theprinting plate; estimating distribution of printing pressure of aprinting plate pressed on a printing medium on the basis of the imagedata and the distribution data of plate thickness; calculating an amountof correction of the relief pattern data on the basis of thedistribution of printing pressure; and correcting the relief patterndata on the basis of the amount of correction.
 2. The platemaking methodaccording to claim 1, wherein the distribution of printing pressure isestimated on the basis of an area ratio of a portion with which theprinting medium is to be brought into contact within a prescribed rangeof the printing plate.
 3. The platemaking method according to claim 1,wherein the relief includes a plurality of protrusions, and the reliefpattern data includes height data and shape data of the plurality ofprotrusions, and wherein the amount of correction of the relief patterndata relates to at least any one of the height data and the shape dataof the plurality of protrusions.
 4. The platemaking method according toclaim 3, wherein each of the plurality of protrusions includes a baseand a tip provided on the base, on which a printing medium is pressed,and wherein the shape data of the plurality of protrusions includes atleast shape data of the tip.
 5. The platemaking method according toclaim 4, wherein the shape data of the tip of each of the plurality ofprotrusions includes data on a portion of the tip that is to be broughtinto contact with the printing medium during printing.
 6. Theplatemaking method according to claim 3, wherein the plurality ofprotrusions includes a base and a tip provided on the base, on which aprinting medium is pressed, and wherein the height data of the pluralityof protrusions relates to any one of tip height, base height, and entireheight of the tip and the base.
 7. The platemaking method according toclaim 1, wherein the relief includes a plurality of protrusions, and therelief pattern data includes volume data of the plurality ofprotrusions, and wherein the amount of correction of the relief patterndata relates to the volume data of the plurality of the protrusions. 8.The platemaking method according to claim 1, further comprising the stepof forming the relief on the printing plate on the basis of the reliefpattern data corrected.
 9. The platemaking method according to claim 8,wherein the relief is formed on the printing plate by exposureprocessing with respect to the printing plate, and exposurecharacteristics related to a thickness direction of the printing plateare derived on the basis of the distribution data of plate thickness sothat the relief is formed on the printing plate by the exposureprocessing in consideration of the exposure characteristics.
 10. Aplatemaking device that forms relief based on relief pattern data in aprinting plate to be pressed on a printing medium, the platemakingdevice comprising: a relief calculation unit that calculates reliefpattern data on the basis of image data; a plate thickness distributionacquisition unit that acquires distribution data of plate thicknessshowing distribution of plate thickness of a printing plate; a printingpressure distribution estimation unit that estimates distribution ofprinting pressure of the printing plate pressed on the printing mediumon the basis of the image data and the distribution data of platethickness; a correction amount calculation unit that calculates anamount of correction of the relief pattern data on the basis of thedistribution of printing pressure; and a data correction unit thatcorrects the relief pattern data on the basis of the amount ofcorrection.
 11. A printing press comprising: the platemaking deviceaccording to claim 10; and a printing unit that presses the printingplate in which relief is formed by the platemaking device on theprinting medium.